Sinai was told to speak to the captain, and if he was busy the lieutenant would also be able to help her. She didnt ant to bother the captain, even though she really really anted to meet him. but he had to be a bust man so she asked the person if they would let the lieutenant know that there was a shinigami interested in joining the squad. the reason she asked that the messaged be passed was because she was certain they wouldnt let just anybody roam around the barracks. it was basically a ninja training camp, probably filed with booby traps, secret passage ways and all kinds of other awesome shit... ok probably not but the thought was entertaining her as she waited.